A cell-free system obtained from tissue cultures of Andrographis paniculata produces 2-trans,6-trans-farnesol (trans, trans-farnesol) and 2-cis,6-trans-farnesol (cis,trans-farnesol) (5:1), incorporating 10% of the radioactivity from 3R-[2-14C]mevalonate. There is total loss of3H from 3RS-[2-14C,(4S)-4-3H1]mevalonate and total retention from the (4R) isomer in both the trans, trans-farnesol and cis,trans-farnesol formed. When 3RS-[2-14C,5-3H2]mevalonate is used as substrate, there is total retention of3H in the trans, trans-farnesol, but loss of one-sixth of the3H in the cis,trans-farnesol. With (1R)- and (1S)-[4,8,12-14C3,1-3H1]-trans, trans -farnesol and (1R)- and (1S)-[4,8,12-14C3,1-3H1]-cis,trans-farnesol as substrates, the label is lost from the (1R)-cis,trans and (1S)-trans, trans isomers but retained in the (1R)-trans, trans and (1S)-cis,trans isomers; this shows that the pro-1S hydrogen is exchanged in the conversion of trans, trans-farnesol into cis,trans-farnesol and the pro-1R hydrogen in the conversion of cis,trans-farnesol into trans, trans-farnesol. (1R)-[1-3H1]-trans, trans-Farnesol and (1R)-[1-3H1]-cis,trans-farnesol have been synthesized by asymmetric chemical synthesis and exchanged with liver alcohol dehydrogenase. Both the trans- and the cis-alcohol exchange the pro-1R hydrogen atom.

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